1. Field of the Embodiments
The embodiments described and illustrated herein are directed to a tool for improving the surveillance performance of wireless receivers in dense co-channel signal environments. The tool is agnostic in that it is able to integrate directly with existing surveillance receiver equipment.
2. Description of the Related Art
The advent of advanced third and fourth generation (3G/4G) wireless cellular and local area network (LAN) radio technology represents a new challenge to lawful electronic surveillance and reconnaissance activities. These new generation radios employ sophisticated waveforms, multichannel processing (MIMO) and powerful error correction coding to maximize reuse of the frequency spectrum while minimizing radio link power between mobile devices and the serving cell transceivers. The resulting dense co-channel interference (CCI) environment prevents all but the closest cell sites from being reliably received by conventional surveillance receivers. Since the cell coverage from a single tower is typically only a 1 to 2 km range, this significantly impacts the available surveillance range. Further, the signals from the distant cell transmitters also interfere with the nearby cell tower signal, reducing its received signal quality as well. This prevents reliable reception of a cell transmitting from the same tower, and also from the sector pointed away from the receiver's location. An adversary can be in close proximity—on the far side of the tower—but remain undetected. Such limitations hamper military, law enforcement and other sensitive operations.
Lawful electronic surveillance operations currently use directional antennas to combat co-channel interference and extend the surveillance range to target cells site transmitters. Two types of directional antenna technologies are used: log-periodic and parabolic reflector (i.e., dish, grid), each optimized for one or more standard wireless frequency bands.
Log periodic (LP) antennas can cover multiple frequency bands simultaneously, so only a single antenna needs to be installed. However, the LP antenna's main beam is generally too broad to be effective in urban/light-urban terrains which have dozens of cell sites lying within the beam.
Parabolic reflector (PR) antennas have had greater success in reducing the co-channel interference background owing to their narrower beam widths. To achieve the narrower beam the PR antennas must be relatively large (˜1 meter diameter) and cover a single operating frequency. Multiple antennas are required to cover standard cell bands, and each must be mechanically steered to each desired cell site in turn. PR antennas will cease to be effective however as the new 4G/LAN technology—LTE, 802.11n, advanced 3G—replace earlier 2G/3G and Wi-Fi formats. Stand-off surveillance of these signals will require multiple antenna elements, spaced within a few wavelengths of each other. A PR antenna cannot achieve this inter-element spacing without widening its beam width, eliminating its CCI mitigation performance.
Accordingly, there remains a need in the art for a system and method for addressing CCI and improving the range and quality of electronic surveillance of wireless cell radio signals across varying terrains and cell site densities.